The present invention relates to a road traffic signal light. Specifically, the present invention relates to an LED signal light for road traffic that is distinguishable by both persons with normal vision and persons with color vision deficiency.
Presently, signal lights, using a light bulb as a light source transmitting light through colored filters of red, yellow, and green, are being replaced by LED signal lights constituted of collections of LED elements of high chromaticity and luminance of red, yellow, and green lights.
An LED signal light, arranged by assembling LED elements that emit light of the same luminance and chromaticity, has a high level of visibility in comparison to a light bulb signal light. It is rapidly spreading in use for the excellence in preventing wash-out caused by morning and afternoon sunlight, resulting from reflected lights against inside mirror.
Meanwhile, the colors of a road traffic signal light are mainly defined based on the visible ability and perception for persons with normal color vision, and adequate considerations have not necessarily been made for color deficient persons who used to distinguish kinds of signals according to brightness differences in case of light bulb type. Especially, since both the luminance and chromaticity in case of LED signal lights are constant and maximize, it has been pointed out that yellow and red appear the same to color deficient persons.
As an LED signal light that is distinguishable by color deficient persons, there is a traffic signal light with the arrangement shown in FIG. 9. With the traffic signal light 101, each of lamps 102, 103, and 104 has a holding plate, holding a plurality of light emitting diodes, and each of lamps 102, 103, and 104 performs lighting display of a different shape according to the configuration of the plurality of light emitting diodes. Specifically, the red lamp 102 displays an X shape by the plurality of light emitting diodes, the yellow lamp 103 displays a triangular shape by lighting of the plurality of light emitting diodes, and the green lamp 104 displays a circular shape by lighting of the plurality of light emitting diodes to enable color deficient persons to distinguish according to lighting shape (see Patent Document 1).
Also, a road traffic signal light shown in FIG. 10 is constituted of plural types of small light sources as 105 and 106 that differ in wavelengths to form a green signal light emitting surface 107, where 108 is a partially enlarged view of the light emitting surface 107. By providing a single green signal light as a whole, distributing of the small light sources 105 and 106, a color deficient person is made to recognize a green signal light (see Patent Document 2).
Patent Document 1: Japanese Published Unexamined Patent Application No. H10-3596 (Abstract, FIG. 1)
Patent Document 2: Japanese Published Unexamined Patent Application No. H8-138192 (Abstract, FIG. 1)
Although with the invention of Patent Document 1, the red, yellow, and green lamps of the traffic signal light are lighted in the X, triangular, and circular shapes to enable a color deficient person to distinguish which lamp is lighted, for a normal vision person, such a traffic signal light is strangely perceived from a normal signal light, and is specifically recognizable as a design for the color deficient person.
Also, the chromaticity and luminance ranges of a traffic signal light are defined by regulations, and when lamps are lighted in the X, triangular, and circular shapes, each lighting area becomes much smaller than a normal signal light area. Therefore, it becomes extremely difficult to secure the prescribed luminance level. It is thus considered that under daylight, a color deficient person may have difficulty in distinguishing which of the red, yellow, and green lamps is lighted.
The invention of Patent Document 2, in order to alleviate misrecognition of a red signal and a green signal by a protan, assembles small light sources of plural types that differ in main wavelength to provide a green signal light, in which lights of no less than two colors are mixed.
Here, among color deficient persons, there are protans and deutans, and although Patent Document 2 described that the number of protans is the highest, in correct actuality, the number incidence of deutan deficiency is the highest and is said to be approximately three times the number of protan deficiency. Also, the document is potentially misleading in that both protans and deutans misrecognize green and red signals. A green signal in Japan, a chromaticity closer to blue is applied for the color deficient person to help distinguishing green from red. Actually, they tend to have a rather high sensitivity to blue, so that erroneous perception between red and yellow is more of a problem in reality.
The signal light of Patent Document 2 is thus aimed at alleviating misrecognition of green by just protans and is not aimed at color deficient persons in general. Also, even if misrecognition is alleviated for just green, as long as the problem of distinguishing between red and yellow remains, the problem of erroneous perception by color deficient persons is not resolved.
The present invention has been made in view of the above points and an objective thereof is to provide a red or a yellow LED signal light with a symbolic pattern based on chromaticities that are distinguishable by color deficient persons even from a certain distance without causing color mixing as a whole.